As the Internet becomes diversified in its capabilities, it becomes feasible to offer services that were not possible under earlier generations of Internet technologies. Real-time multimedia streaming and IP multicast are two such emerging technologies. The development and use of commercial applications based on these technologies, such as Internet telephony, will become increasingly prevalent, and their traffic will constitute a large portion of the Internet traffic in the future.
Congestion and flow control are integral parts of any Internet data transport protocol whose traffic travels a shared network path. It is widely accepted that the congestion avoidance mechanisms employed in TCP have been one of the key contributors to the success of the Internet. However, few commercial streaming applications today are equipped with end-to-end flow control. The traffic generated by these applications is unresponsive to congestion and can completely lock out other competing flows, monopolizing the available bandwidth. The destructive effect of such traffic on the Internet commonwealth is commonly referred to as congestion collapse.
TCP is ill-suited for real-time multimedia streaming applications because of their real-time and loss-tolerant natures. The bursty transmission, and abrupt and frequent deep fluctuations in the transmission rate of TCP cause delay jitters and sudden quality degradation of multimedia applications. For asymmetric networks, such as wireless networks, cable modems, ADSL, and satellite networks, transmitting feedback for (almost) every packet received as it is done in TCP is not advantageous because of lack of bandwidth on the reverse links. In asymmetric networks, packet losses and delays occurring in reverse paths severely degrade the performance of existing round trip based protocols, such as TCP, resulting in reduced bandwidth utilization, fairness, and scalability. The use of multicast further complicates the problem: in large-scale multicast involving many receivers (10,000 to 1M receivers), frequent feedback sent directly to the sender causes the sender to be overwhelmed acknowledgment messages. Accordingly, there exists a long-felt need for methods and systems for end-to-end flow control that avoid the difficulties associated with conventional flow control protocols.